The present invention relates to the fabrication of Single-In-Line semiconductor devices, especially in a molded plastic package.
A large number of semiconductor devices are produced in so-called Single-In-Line (SIL) type packages of various shapes wherein all the pins of the device emerge from the same side of the package and are bent by pressing them between a pair of punches, respectively a bending and a contrasting punch, suitably set in a press. This is done both in the case of packages wherein all the pins remains coplanar as well as in packages wherein the pins are "splitted" in two orders or rows of pins, which once bent, become arranged on two parallel planes, spaced from each other.
The bending of the pins normally takes place at the end of the encapsulating process of the device as the last mechanical operation, naturally carried out in an automatic manner. Most often the devices so produced present their pins slanting in a more or less uniform manner toward one side instead of being correctly perpendicular to the face of the container from which they project. This slanting off from a correct perpendicular orientation of the pins, even if uniform, may cause inconveniences during the assembly of the devices on printed circuit cards, which is normally carried out by robots.
It has been observed that the cause of said lateral slanting of the pins during the bending of the same is due to lack of planarity and parallelism of their top and bottom surfaces which are engaged, respectively, by the bending punch and by the contrasting punch during the bending operation. The combined action of the two punches acting on faces which are not parallel to each other tends to twist laterally the pin upon bending it. A deformation of the cross section of the pins is often caused by die stamping the thin metal sheet, commonly of copper or of nickel plated copper, for patterning the assembly metal frame of the semiconductor chip through which also the pins are generated, which once the minuscule metal bridges left by the die stamping are eventually broken, will constitute the "isolated" pins of the device. The die stamping tends to deform in a similar but not identical way the cross section of all the pins thus causing different torsional and flexural moments upon the bending thereof. The problem worsens with the wearing of the die stamping punches.